People elected to be national leaders all grasp a basic concept like the MAD doctrine, and no developed nation's leader has the authority to single-handedly initiate a nuclear strike.

This isn't some cartoon shit where Trump is handed a fat red button that says "NUKE" and hammers it whenever he gets angry.

No nuclear war is going to happen unless the target has been systematically disarmed and the transgressor actually benefits from proceeding to nuke them, or you get a volatile nation like NK pushed into a corner where they attack with their flimsy rockets as a last resort.

That is true and I was being pretty generalizing. But I remember seeing an interview with one of Obama’s advisors after the 2016 election. He seemed distraught and kept saying there is no second opinion or failsafe on the presidents actions. Trump seems to surround himself with an administration that can’t even talk him out of tweeting. I guess the point I was trying to make is that if world leaders are moving in that direction the world does become a less safe place.

It's true to some extent, someone has to dissent to prevent a nuclear attack request from the US president.

But at the very least, this means that the president does not hold the full ability to plan and launch a nuclear strike by himself - it has to go through others, who will always at least have the option to decline.

The US president has the authority to request a nuclear strike, but it has to go through several parties first.

While the secretary of defense technically isn't allowed to veto an order, they still need to verify it before it goes through. They can, in other words, take one for the team and decline a retarded world-ending request.

I have so little faith in the system that I don’t think anyone would actually have the balls to tell President Trump he can’t fire the missiles. There would be plenty of “but sir”’s but inevitably those nukes will launch. No way the president is sitting in a nuke scenario and not racing for first strike.

I think Putin ultimately would if he knew that there would be little retaliation. Russian policy has always been open to the possibility of tactical nuclear strikes in a conventional war, compared to the US's MAD policy. Against targets like Iran or North Korea, official policy is that it wouldn't be off the table.
NK is purely using theirs as a deterrent to stop a potential Coup or invasion by South Korea, as well as to establish dominance domestically.
I think Trump would, but everyone around him wouldn't let him, therefore he wouldn't. He'd also never do it unprovoked, but if his ego's hurt, and he has the chance, it's not off the table.